https://bugs.freedesktop.org/show_bug.cgi?id=61993

--- Comment #4 from Luke <[email protected]> ---
Correction, the LibreOffice formula (from code) is:

77*red + 151*green + 28*blue <= 38*256

I notice that both Word and LibreOffice formulae use weights proportional to
the "Rec. 601" coefficients for Luma shown here:
http://en.wikipedia.org/wiki/Luma_%28video%29
ie Luma = 0.299 R' + 0.587 G' + 0.114 B'

(Actually LibreOffice would match these coefficients more accurately if it used
 76*red + 151*green + 29*blue)

Anyway the main difference is that LibreOffice considers Luma <= 38 (out of
255) to be dark, whereas Word considers Luma < about 61 (out of 255) to be
dark.

The formula I put forward earlier for Word is very slightly off, because of the
following data points:
(red=61, green=61, blue=60) is not dark
(red=60, green=61, blue=61) is dark

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